Musnad Ahmad 1012:96

Mu'awiyah ibn 'Amr narrated to us, Abu Ishaq narrated to us, from 'Abd al-Rahman ibn 'Ayyash ibn Abi Rabi'ah, from Sulayman ibn Musa, from Abu Salam, from Abu Umamah, from 'Ubadah ibn al-Samit, who said: We went out with the Prophet, may Allah bless him and grant him peace, and I witnessed the Battle of Badr with him. The people met, and Allah defeated the enemy. A group set out in their tracks, defeating and killing them. A group crowded around the camp, gathering and collecting it. A group surrounded the Messenger of Allah, may Allah bless him and grant him peace, so that the enemy would not find an opening to reach him. When night fell and the people returned to one another, those who had gathered the spoils said: "We gathered and collected them, so no one else has a share in them." Those who had gone out in pursuit of the enemy said: "You are no more entitled to them than we are; we drove the enemy away from them and defeated them." Those who had surrounded the Messenger of Allah, may Allah bless him and grant him peace, said: "You are no more entitled to them than we are; we surrounded the Messenger of Allah, may Allah bless him and grant him peace, fearing that the enemy might find an opening to reach him, and we were occupied with him." Then it was revealed: "They ask you about the spoils of war. Say, 'The spoils of war are for Allah and the Messenger.' So fear Allah and amend that which is between you" [Al-Anfal: 1]. So the Messenger of Allah, may Allah bless him and grant him peace, divided them equally among the Muslims. He said: When the Messenger of Allah, may Allah bless him and grant him peace, would raid the land of the enemy, he would grant a fourth as extra spoils (nafal), and when he returned, and all the people were together, he would grant a third. He used to dislike the extra spoils and would say: "Let the strong among the believers give back to their weak."